Glossary

<< Appendix E: Solar Dimensioning:General Data, Component Characteristics

Glossar y

0-9

A d d re s s R e s o l u t i o n P ro t o c o l

802.11.While802.11 is a wireless

(ARP).A protocolwidely used on

protocol in its own right, 802.11 is

Ethernetnetworks to translate IP

oftenused to refer to a family of wire-

addressesinto MAC addresses.

lessnetworking protocolsused

mainlyfor local areanetworking.

addressspace. A group of IP ad-

Threepopular variantsinclude

dressesthat all reside withinthe

802.11b, 802.11g, and 802.11a. See

also:Wi-Fi.

samelogical subnet.

advertisedwindow. Theportion of

a TCP header thatspecifies how

manyadditional bytes of datathe

receiver is prepared to accept.

AC seeAlternatingCurrent

AlternatingCurrent (AC). An elec-

tricalcurrent which varies overtime

accesspoint (AP). A devicethat

in a cyclic manner. AC current is

creates a wireless network that is

typicallyused for lighting andappli-

usuallyconnected to a wired

ances.See also: DirectCurrent

Ethernetnetwork. See also:CPE,

mastermode

amortization.An accountingtech-

niqueused to manage theexpected

accumulator.Anothername for a

cost of replacement andobsoles-

battery.

cence of equipment overtime.

ad-hocmode. A radiomode used

amplifier.A deviceused to increase

by 802.11 devices that allowsthe

thetransmitted power of a wireless

creation of a network without an ac-

device.

cesspoint. Mesh networksoften

useradios in ad-hoc mode.See

amplitude. Thedistance from the

also:managedmode, master

center of a wave to the extreme of

mode,monitor mode

one of its peaks.

389

390

Glossary

anchorclients. Businessclients of

coordinates,logarithmic polar

coordinates

a subscription system who arereli-

ableand can be consideredlow-risk.

AP seeAccessPoint

ANDlogic. A logicaloperation that

applicationlayer. Thetopmost

onlyevaluates as true if all of the

itemsbeing compared alsoevaluate

layer in the OSI and TCP/IPnetwork

as true. See also:OR logic.

models.

anonymizingproxy. A networkserv-

ArgusseeAuditRecord Generation

andUtilization System

icethat hides the source or destina-

tion of communications. Anonymizing

ARPseeAddressResolution

proxiescan be used to protectpeo-

Protocol

ple'sprivacy and to reduce an or-

ganization'sexposure to legalliability

associated.An 802.11radio is as-

forthe actions of itsusers.

sociated to an access point when it is

anonymity.In computernetworks,

ready to communicate with the net-

communicationsthat cannot be

work.This means that it is tuned to

linked to a unique individualare

theproper channel, in range of the

said to be anonymous. Thetrade-

AP,using the correct SSIDand other

off of anonymity versusaccount-

authenticationparameters, etc.

ability in communications is an on-

at.A Unixfacility that allowstimed,

goingdebate online, andrules

aboutanonymous communications

one-shotexecution of programs.

Seealso: cron

varywidely around the world.See

also:authenticated

attenuation.Thereduction of avail-

antennadiversity.

A technique

ableradio power as it is absorbed

used to overcome multipathinterfer-

along a path, such as throughtrees,

ence by using two or morephysi-

walls,buildings, or other objects.See

also:freespace loss,scattering

callyseparated receivingantennas.

antennagain. Theamount of

AuditRecord Generationand

UtilizationSystem (Argus). An

powerconcentrated in thedirection

of strongest radiation of an antenna,

opensource network monitoringtool

usuallyexpressed in dBi.Antenna

usedfor tracking flowsbetween

gain is reciprocal, which meansthat

hosts.Argus is availablefrom

http://www.qosient.com/argus.

theeffect of gain is presentwhen

transmitting as well as receiving.

authenticated.A networkuser that

antennapattern. A graphthat de-

hasproven their identity to a service

scribesthe relative strength of a

or device (such as an accesspoint)

radiatedfield in various directions

beyond a shadow of a doubt,usually

from an antenna. See also:rectan-

by some means of cryptography.

gularplot, polar plot, linearpolar

Seealso: anonymity

Glossary

391

azimuth.Theangle that measures

connectorsare typically found on

10base2coaxial Ethernet.

deviationwith respect to the south in

thenorthern hemisphere, andwith

bridge.A networkdevice that con-

respect to the north in thesouthern

hemisphere.See also: inclination

nectstwo networks together at the

data link layer.

Bridges do not

routepackets at the networklayer.

Theysimply repeat packetsbetween

twolink-localnetworks.See also:

routerandtransparentbridging

bandwidth.

A measure of fre-

firewall.

quencyranges, typically usedfor

digitalcommunications. Theword

bridge-utils.A Linuxsoftware

bandwidth is also commonly used

interchangeablywith capacityto

packagethat is required forcreat-

ing802.1d Ethernetbridges.

refer to the theoreticalmaximum

http://bridge.sourceforge.net/

datarate of a digitalcommunica-

tionsline. See also:capacity,

BroadbandGlobal AccessNet-

channel,throughput

work(BGAN). One of several stan-

battery.A deviceused to store en-

dardsused for satellite Internetac-

Seealso: DigitalVideo

cess.

ergy in a photovoltaic system.See

Broadcast(DVB-S) andVerySmall

also:solarpanel, regulator,load,

ApertureTerminal (VSAT).

converter,inverter

broadcastaddress. On IP net-

beamwidth.Theangular distance

works,the broadcast IP address is

betweenthe points on either side of

used to send data to all hosts in the

themain lobe of an antenna,where

localsubnet. On Ethernetnetworks,

thereceived power is half that of the

thebroadcast MAC address is used

mainlobe. The beamwidth of an

to send data to all machines in the

antenna is usually stated forboth

samecollision domain.

thehorizontal and verticalplanes.

bypassdiodes. A featurefound on

benchmarking.Testingthe maxi-

somesolar panels that preventsthe

mumperformance of a service or

formation of hot-spotson shaded

device. Benchmarking a network

cells,but reduces themaximum

connectiontypically involves flood-

voltage of the panel.

ingthe link withtraffic andmeasur-

ingthe actual observedthroughput,

both on transmit andreceive.

BGANseeBroadbandGlobal Ac-

cessNetwork

CA seeCertificateAuthority

BNCconnector. A coaxial cable

Cacti (http://www.cacti.net/). A

connectorthat uses a "quick-

popularweb-based monitoringtool

connect"style bayonet lug.BNC

written in PHP.

392

Glossary

capacity.Thetheoretical maximum

can be specified as /24 in CIDR no-

amount of traffic provided by a digi-

tation.

talcommunications line. Oftenused

interchangeablywith bandwidth.

circular polarization. An electro-

magneticfieldwhere the electric

captiveportal. A mechanismused

fieldvector appears to be rotating

to transparently redirect webbrows-

withcircular motion about thedirec-

ers to a new location. Captivepor-

tion of propagation, making onefull

talsare often used forauthentication

turnfor each RF cycle. Seealso:

horizontalpolarization, vertical

or for interrupting a user'sonline

polarization

session(for example, to display an

AcceptableUse Policy).

Class A, B, and C networks. For

cell.Solarpanels are made up of

sometime, IP address spacewas

severalindividual cells, whichare

allocated in blocks of threedifferent

electricallyconnected to provide a

sizes. These were Class A (about

particularvalue of current andvolt-

16 million addresses), Class B

age.Batteries are also made up of

(about 65 thousand addresses),and

individualcells connected in series,

Class C (255 addresses).

While

each of which contributes about 2

CIDRhas replaced class-basedal-

volts to the battery.

location,these classes are oftenstill

referred to and used internally in

CertificateAuthority. A trusteden-

organizationsusing private address

space.See also: CIDRnotation.

titythat issues signedcryptographic

keys.See also: PublicKey Infra-

ClasslessInter-Domain Routing.

structure,SSL

CIDRwas developed to improve

channelcapacity. Themaximum

routingefficiency on theInternet

backbone by enabling routeaggrega-

amount of information that can be

tionand network masks of arbitrary

sentusing a given bandwidth.See

also:bandwidth,throughput,

size. CIDR replaces the oldclass-

datarate

basedaddressing scheme.

See

also:Class A, B, and C networks.

channel.A well definedrange of

client.An 802.11radio card in

frequenciesused for communica-

managedmode. Wirelessclients

tions.802.11 channels use 22 MHz

willjoin a network created by an

of bandwidth, but are onlyseparated

by 5 MHz. See also:Appendix B.

accesspoint, andautomatically

changethe channel to match it.See

CIDRseeClasslessInter-Domain

also:accesspoint, mesh

Routing

closednetwork. An accesspoint

CIDRnotation. A methodused to

thatdoes not broadcast itsSSID,

define a network mask by specifying

oftenused as a securitymeasure.

thenumber of bits present. Forex-

ample,the netmask255.255.255.0

Glossary

393

coax.A round(coaxial) cable with a

controls.In NEC2, controls define

centerwire surrounded by a dielec-

the RF source in an antennamodel.

Seealso: structure

tric,outer conductor, and toughinsu-

latingjacket. Antenna cablesare

converter.A deviceused to convert

usuallymade of coax. Coax is short

for"of common axis".

DC signals into a different DC or AC

voltage.See also: inverter

collision.On an Ethernetnetwork, a

CPE seeCustomerPremises

collisionoccurs when twodevices

Equipment

connected to the same physical

segmentattempt to transmit at the

cron.

sametime. When collisions arede-

A Unix facility thatallows

tected,devices delayretransmission

timedand repeated execution of

programs.See also: at

for a brief, randomly selectedperiod.

conductor.A materialthat easily

CustomerPremises Equipment.

allowselectric or thermal energy to

Networkequipment (such as a

routeror bridge) that is installed at

flowthrough without muchresis-

tance.See also: dielectric,insulator

a customer's location.

connectionlessprotocol. A network

protocol(such as UDP) thatrequires

no session initiation or maintenance.

Connectionlessprotocols typically

data link layer. Thesecond layer in

requireless overhead thansession

boththe OSI and TCP/IPnetwork

orientedprotocols, but do notusually

models.

Communications at this

offer data protection or packet reas-

layerhappen directlybetween

sembly.See also: sessionoriented

nodes. On Ethernet networks,this

protocol.

is also sometimes called theMAC

layer.

consistentplatform. Maintenance

costscan be reduced by using a

datarate. Thespeed at which

consistentplatform, with thesame

802.11radios exchangesymbols,

hardware,software, and firmware

which is always higher thanthe

formany components in a network.

availablethroughput. Forexample,

thenominal data rate of 802.11g is

constructiveinterference. When

54 Mbps, while the maximum

twoidentical waves merge andare

throughput is about 20 Mbps).See

in phase, the amplitude of theresult-

also:throughput

ingwave is twice that of either of the

components.This is calledconstruc-

dB seedecibel

tiveinterference. See also:destruc-

tiveinterference

DC seeDirectCurrent

DC/ACConverter. A devicethat

converts DC power into AC power,

394

Glossary

DHCPseeDynamicHost Configu-

suitablefor use with manyappli-

ances.Also known as an inverter.

rationProtocol

DC/DCConverter. A devicethat

dielectric.A non-conductive mate-

changesthe voltage of a DC power

rialthat separates conductingwires

source.See also: linearconver-

inside a cable.

sion,switching conversion

DigitalElevation Map (DEM). Data

decibel(dB). A logarithmicunit of

thatrepresents the height of terrain

measurementthat expresses the

for a given geographic area.These

magnitude of power relative to a

mapsare used by programs such as

RadioMobile to modelelectromag-

referencelevel. Commonly used

unitsare dBi (decibels relative to an

neticpropagation.

isotropicradiator) and dBm(deci-

DigitalVideo Broadcast(DVB-S).

belsrelative to a milliwatt).

One of several standards usedfor

defaultgateway. When a router

satelliteInternet access. Seealso:

BroadbandGlobal AccessNet-

receives a packet destined for a

work(BGAN) andVerySmall Ap-

networkfor which it has no explicit

ertureTerminal (VSAT).

route,the packet is forwarded to the

defaultgateway. The defaultgate-

dipoleantenna. Thesimplest form

waythen repeats the process,pos-

of omnidirectionalantenna.

siblysending the packet to itsown

defaultgateway, until thepacket

DirectCurrent (DC). An electrical

reachesits ultimatedestination.

currentwhich remains constantover

defaultroute. A networkroute that

time. DC current is typically usedfor

points to the defaultgateway.

networkequipment, such as access

pointsand routers. See also:Alter-

Denial of Service (DoS). An attack

natingCurrent

on network resources,usually

DirectSequence SpreadSpec-

achieved by flooding a network with

trum(DSSS). Theradio modulation

traffic or exploiting a bug in an appli-

cation or network protocol.

schemeused by 802.11b.

depreciation.An accounting

directionalantenna. An antenna

methodused to save money to

thatradiates very strongly in a par-

coverthe eventual break down of

ticulardirection. Examples of direc-

equipment.

tionalantennas include theyagi,

dish,and waveguide antennas.See

destructiveinterference. When

also:omnidirectionalantenna,

sectorialantenna

twoidentical waves merge andare

exactlyout of phase, theamplitude

directivity.Theability of an antenna

of the resulting wave is zero.This is

calleddestructive interference.See

to focus energy in a particulardirec-

also:constructiveinterference

tionwhen transmitting, or to receive

Glossary

395

edge.Theplace where oneorgani-

energyfrom a particulardirection

whenreceiving.

zation'snetwork meetsanother.

Edgesare defined by the location of

diversityseeantennadiversity

theexternal router, whichoften acts

as a firewall.

DNSseeDomainName Service

electromagneticspectrum. The

DNScaching. By installing a DNS

verywide range of possiblefre-

server on your local LAN, DNSre-

quencies of electromagnetic energy.

questsfor an entire network may be

Parts of the electromagneticspec-

cachedlocally, improvingresponse

truminclude radio, microwave,visi-

times.This technique is calledDNS

blelight, and X rays.

caching.

electromagneticwave. A wavethat

dnsmasq.An opensource caching

propagatesthrough space without

DNSand DHCP server,available

theneed for a propagatingmedium.

fromhttp://thekelleys.org.uk/

It contains an electric and a mag-

neticcomponent. See also:me-

DomainName Service (DNS).The

chanicalwave

widelyused network protocolthat

elevationseeinclination

maps IP addresses to names.

dominantmode. Thelowest fre-

endspan injectors. An 802.3af

Powerover Ethernet devicethat

quencythat can be transmitted by a

waveguide of a given size.

providespower via the Ethernetca-

ble. An Ethernet switch thatprovides

DoSseeDenial of Service

power on each port is an example of

an end span injector. Seealso: mid

DSSS see DirectSequence

spaninjectors

SpreadSpectrum

end-to-endencryption. An en-

DVB-SseeDigitalVideo Broadcast.

cryptedconnection negotiated by

bothends of a communicationsses-

DynamicHost ConfigurationPro-

sion.End-to-end encryptioncan

tocol(DHCP). A protocolused by

providestronger protection thanlink

layerencryption whenused on

hosts to automatically determine

their IP address.

untrustednetworks (such as the

Internet).

EtherApe.An opensource network

visualizationtool.

Available at

http://etherape.sourceforge.net/

eavesdropper.Someonewho inter-

ceptsnetwork data such as pass-

EtherealseeWireshark.

words,email, voice data, or online

chat.

396

Glossary

ExtendedService Set Identifier

ingloops need to be resolvedfor

(ESSID).Thename used to identify

propernetwork operations.

an 802.11 network. Seealso:

closednetwork

freespace loss. Powerdiminished

by geometric spreading of thewave-

externaltraffic. Networktraffic that

front, as the wavepropagates

throughspace. See also:attenua-

originatesfrom, or is destined for, an

tion,free space loss, Appendix C

IP address outside yourinternal

network,such as Internet traffic.

frequency.Thenumber of whole

wavesthat pass a fixedpoint in a

period of time. See also:wave-

length,Hertz

firestarter.A graphicalfront-end for

front-to-backratio. Theratio of the

configuringLinux firewallsavailable

maximumdirectivityof an antenna

fromhttp://www.fs-security.com/.

to its directivity in theopposite direc-

tion.

filter.Thedefault table used in the

Linuxnetfilterfirewallsystem is the

fullduplex. Communications

filtertable. This table is used for

equipmentthat can send andre-

determiningtraffic thatshould be

ceive at the same time (such as a

accepted or denied.

telephone).See also: halfduplex

firewall. A routerthat accepts or

fwbuilder.A graphicaltool that lets

deniestraffic based on some crite-

youcreate iptablesscripts on a

ria. Firewalls are onebasic tool

machineseparate from yourserver,

used to protect entire networksfrom

andthen transfer them to theserver

undesirabletraffic.

later.http://www.fwbuilder.org/

flush. To remove all entries in a

routingtable or netfilterchain.

forwarding.Whenrouters receive

gain.Theability of a radiocompo-

packetsthat are destined for a dif-

ferenthost or network, they sendthe

nent(such as an antenna or ampli-

packet to the next router closest to

fier) to increase the power of a sig-

nal.See also: decibel

itsultimate destination. Thisprocess

is called forwarding.

gaintransfer. Comparing an an-

forwardingloops. A routing mis-

tennaunder test against a known

configurationwhere packets are

standardantenna, which has a cali-

forwardedcyclically between two or

bratedgain.

morerouters. Catastrophicnetwork

gasification.Theproduction bub-

failure is prevented by using theTTL

value on every packet, butforward-

bles of oxygen and hydrogenthat

Glossary

397

occurswhen a battery is over-

zontaldirection. See also:circular

charged.

polarization,vertical polarization

globallyroutable. An addressis-

hot-spot.In wirelessnetworks, a

sued by an ISP or RIR that is reach-

hot-spot is a location thatprovides

Internetaccess via Wi-Fi, typically

ablefrom any point on theInternet.

by use of a captiveportal. In pho-

In IPv4, there areapproximately four

tovoltaicsystems, a hot-spotoc-

billionpossible IP addresses,al-

curswhen a single cellin a solar

thoughnot all of these areglobally

panelis shaded,causing it to act as

routable.

a resistive load rather than to gen-

eratepower.

hub.An Ethernetnetworking device

half duplex. Communications equip-

thatrepeats received data on all

connectedports. See also:switch.

ment that can send or receive, but

never both at once (such as a hand-

Huygensprinciple. A wavemodel

heldradio). See also:full duplex.

thatproposes an infinitenumber of

Heliax.Highquality coaxial cable

potentialwavefronts alongevery

point of an advancing wavefront.

thathas a solid or tubularcenter

conductorwith a corrugatedsolid

Hz seeHertz

outerconductor which enables it to

flex.See also: coax

Hertz(Hz). A measure of fre-

quency, denotingsome number of

IANAseeInternetAssigned Num-

cyclesper second.

bersAuthority

HF (High-Frequency).

Radio

ICMPseeInternetControl Mes-

wavesfrom 3 to 30 MHz arere-

sageProtocol

ferred to as HF. Data networkscan

be built on HF that operate at very

ICPseeInter-CacheProtocol

longrange, but with verylow data

capacity.

impedance.Thequotient of voltage

hop.Datathat crosses onenetwork

overcurrent of a transmissionline,

connection. A web server may be

consisting of a resistance and a re-

severalhops away from yourlocal

actance.The load impedancemust

computer, as packets areforwarded

matchthe source impedancefor

fromrouter to router,eventually

maximumpower transfer (50 for

reachingtheir ultimatedestination.

mostcommunications equipment).

horizontalpolarization. An elec-

inboundtraffic. Networkpackets

tromagneticfieldwith the electric

thatoriginate from outside thelocal

componentmoving in a linearhori-

network(typically the Internet)and

398

Glossary

IntrusionDetection System(IDS).

arebound for a destinationinside

thelocal network. Seealso: out-

A program that watchesnetwork

boundtraffic.

traffic, looking for suspicious data or

behaviorpatterns.

An IDS may

inclination. Theangle that marks

make a log entry, notify a network

deviationfrom a horizontalplane.

administrator, or take direct action in

Seealso: azimuth

response to undesirable traffic.

infrastructuremode seemaster

inverterseeDC/ACConverter

mode

IP seeInternetProtocol

insulatorseedielectric

iproute2.

Theadvanced routing

Inter-CacheProtocol (ICP). A high

toolspackage for Linux, usedfor

traffic shaping and otheradvanced

performanceprotocol used to com-

techniques.

Available from

municatebetween web caches.

http://linux-net.osdl.org/

Internet Assigned Numbers

iptables.

Authority(IANA). Theorganization

Theprimary command

used to manipulate netfilterfirewall

thatadministers various criticalparts

rules.

of Internet infrastructure,including

IP address allocation, DNSroot

irradiance.Thetotal amount of so-

nameservers, and protocolservice

larenergy that lights a givenarea, in

numbers.

W/m2

InternetControl MessageProto-

ISM band. ISM is short for Indus-

col(ICMP). A NetworkLayer proto-

trial,Scientific, andMedical. The

colused to inform nodes aboutthe

ISMband is a set of radiofrequen-

state of the network. ICMP is part of

ciesset aside by the ITUfor unli-

theInternet protocolsuite.

See

also:Internetprotocol suite.

censeduse.

Internetlayer seenetworklayer

isotropicantenna. A hypothetical

antennathat evenlydistributes

InternetProtocol (IP). The mostcom-

power in all directions,approximated

monnetwork layer protocol in use. IP

by a dipole.

defines the hosts and networks that

IV characteristic curve. A graph

make up the global Internet.

thatrepresents the current that is

Internetprotocol suite(TCP/IP).

providedbased on the voltagegen-

eratedfor a certain solarradiation.

Thefamily of communicationproto-

colsthat make up theInternet.

Some of these protocolsinclude

TCP,IP, ICMP, andUDP.

Also

calledthe TCP/IPprotocol suite, or

simplyTCP/IP.

Glossary

399

Line of Sight (LOS). If a person

standing at point A has an unob-

structedview of point B, then point A

is said to have a clear Line of Sight

knetfilter.A graphicalfront-end for

to point B.

configuringLinux firewalls.Available

fromhttp://venom.oltrelinux.com/

linearpolar coordinates. A graph

systemwith equally spaced,gradu-

knowngood. In troubleshooting, a

atedconcentric circlesrepresenting

knowngood is any componentthat

an absolute value on a polarprojec-

can be substituted to verify thatits

tion.Such graphs are typicallyused

counterpart is in good, working

to represent antenna radiationpat-

condition.

terns.See also: logarithmicpolar

coordinates

linearconversion. A DC voltage

conversionmethod that lowersthe

lag.Commonterm used to describe

voltage by converting excessenergy

a network with highlatency.

to heat. See also:switchingcon-

version

lambda ( ) seewavelength

linearpolarization. An electro-

LANseeLocalArea Network

magneticwave wherethe electric

fieldvector stays in the sameplane

latency.Theamount of time it takes

allthe time. The electricfieldmay

for a packet to cross a networkcon-

leavethe antenna in a verticalorien-

nection. It is often (incorrectly)used

tation, a horizontal orientation, or at

interchangeablywith Round Trip

someangle between the two.See

Time(RTT), since measuringthe

also:verticalpolarization, hori-

RTT of a wide-area connection is

zontalpolarization

trivialcompared to measuringthe

actuallatency. See also:Round

link budget. Theamount of radio

TripTime.

energyavailable to overcomepath

losses. If the available linkbudget

lead-acidbatteries. Batteriescon-

exceedsthe path loss,minimum

sisting of two submerged leadelec-

receivesensitivity of thereceiving

trodes in an electrolytic solution of

radio,and any obstacles,then

waterand sulfuric acid. Seealso:

communicationsshould be possible.

stationarybatteries

link layer encryption. An encrypted

leasetime. In DHCP, IP addresses

connectionbetween link-localde-

areassigned for a limitedperiod of

vices,typically a wireless clientand

time,known as the lease time.After

an accesspoint. Seealso: end-to-

thistime period expires, clientsmust

endencryption

request a new IP address fromthe

DHCPserver.

400

Glossary

link-local.Networkdevices that are

connected to the same physical

segmentcommunicate with each

otherdirectly are said to be link-

MAClayer seedata link layer

local. A link-local connectioncannot

cross a router boundary withoutus-

MACaddress. A unique 48 bit number

ingsome kind of encapsulation,

assigned to every networkingdevice

such as a tunnelor a VPN.

when it is manufactured. The MAC ad-

dress is used for link-localcommunica-

listen. Programsthat accept con-

tions.

nections on a TCP port are said to

MACfiltering.An accesscontrol

listen on that port.

methodbased on the MACaddress

load.Equipment in a photovoltaic

of communicating devices.

systemthat consumes energy.See

MACtable. A networkswitch must

also:battery,solar panel,regula-

tor,converter, inverter

keeptrack of the MACaddresses

used on each physical port, in order

LocalArea Network (LAN).A net-

to efficientlydistribute packets.This

information is kept in a tablecalled

work(typically Ethernet) usedwithin

theMAC table.

an organization. The part of a net-

workthat exists just behind an ISP's

maintenance-freelead-acid bat-

router is generally considered to be

teriesseelead-acidbatteries

part of the LAN. See also:WAN.

Man-In-The-Middle(MITM). A

logarithmicpolar coordinates. A

networkattack where a malicious

graphsystem withlogarithmically

userintercepts allcommunications

spaced,graduated concentriccircles

between a client and a server,allow-

representing an absolute value on a

inginformation to be copied or ma-

polarprojection. Such graphsare

nipulated.

typicallyused to representantenna

radiationpatterns. See also:linear

managedhardware. Networking

polarcoordinates

hardwarethat provides an adminis-

longfat pipe network. A network

trativeinterface, portcounters,

SNMP, or other interactivefeatures

connection(such as VSAT) thathas

is said to be managed.

highcapacity and high latency. In

order to achieve the bestpossible

managedmode. A radiomode

performance,TCP/IP must be tuned

used by 802.11 devices thatallows

to match the traffic on suchlinks.

theradio to join a networkcreated

by an access point. See also:mas-

LOSseeLine of Sight

termode, ad-hoc mode,monitor

mode

Glossary

401

masterbrowser.

mesh.A networkwith no hierarchi-

On Windows

networks,the master browser is the

calorganization, where everynode

computerthat keeps a list of allthe

on the network carries thetraffic of

computers,shares and printersthat

everyother as needed. Goodmesh

areavailable in NetworkNeighbor-

networkimplementations areself-

hoodor My Network Places.

healing,which means thatthey

automaticallydetect routing prob-

mastermode. A radiomode used

lemsand fix them as needed.

by 802.11 devices that allowsthe

messagetypes. Ratherthat port

radio to create networks just as an

accesspoint does. See also:man-

numbers,ICMP traffic usesmes-

agedmode, ad-hoc mode,moni-

sagetypes to define thetype of in-

tormode

formationbeing sent.

Seealso:

ICMP.

matchcondition.

In netfilter, a

method of the worst month.A

matchcondition specifies thecriteria

thatdetermine the ultimatetarget for

methodfor calculating thedimen-

a given packet. Packetsmay be

sions of a standalone photovoltaic

matched on MAC address,source

system so it will work in the month in

or destination IP address, portnum-

whichthe demand for energy is

ber,data contents, or just aboutany

greatestwith respect to theavailable

otherproperty.

solarenergy. It is the worstmonth of

theyear, as this month withhave the

MaximumDepth of Discharge

largestratio of demanded energy to

(DoDmax). Theamount of energy

availableenergy.

extractedfrom a battery in a single

MHF seeU.FL

dischargecycle, expressed as a

percentage.

microfinance.Theprovision of

smallloans, savings and otherbasic

MaximumPower Point (Pmax). The

financialservices to the world s

pointwhere the power supplied by a

poorestpeople.

solarpanel is at maximum.

midspan injectors. A Powerover

MC-Card.A verysmall microwave

Ethernetdeviceinserted between

connector found on Lucent / Orinoco /

an Ethernet switch and thedevice to

Avayaequipment.

be powered. See also:endspan

injectors

mechanicalwave. A wavecaused

whensome medium or object is

milliwatts(mW). A unit of power

swinging in a periodic manner.See

representingone thousandth of a

also:electromagneticwave

Watt.

MediaAccess Control layersee

MITM seeMan-In-The-Middle

data link layer

402

Glossary

MMCX.A verysmall microwave

doornetworking components,such

connectorcommonly found on

as antennas and outdooraccess

equipmentmanufactured by Senao

points.

andCisco.

Nagios(http://nagios.org/) A real-

monitormode. A radiomode used

timemonitoring tool that logsand

by 802.11 devices not normallyused

notifies a system administrator

forcommunications that allowsthe

aboutservice and networkoutages.

radiopassively monitor radiotraffic.

Seealso: mastermode, managed

NATseeNetworkAddress Trans-

mode,ad-hoc mode

lation

monitorport.

nat.Thetable used in theLinux

On a managed

switch,one or more monitorports

netfilterfirewallsystem to configure

may be definedthat receive traffic

NetworkAddress Translation.

sent to all of the other ports.This

NEC2seeNumericalElectromag-

allowsyou to connect a traffic moni-

neticsCode

torserver to the port to observe and

analyzetraffic patterns.

NetBIOS.A sessionlayer protocol

MultiRouter Traffic Grapher

used by Windows networking for file

(MRTG).An opensource tool used

andprinter sharing. See also:SMB.

forgraphing traffic statistics.Avail-

netfilter.

ablefrom http://oss.oetiker.ch/mrtg/

Thepacket filtering

framework in modern Linuxkernels

multipath.Thephenomenon of re-

is known as netfilter. It uses the

flections of a signal reaching their

iptablescommand to manipulate

filterrules. http://netfilter.org/

targetalong different paths,and

therefore at different times.

netmask(networkmask). A net-

multipoint-to-multipointsee

mask is a 32-bit number thatdivides

mesh

the 16 million available IP addresses

intosmaller chunks, calledsubnets.

mW seemilliwatt

All IP networks use IP addresses in

combinationwith netmasks to logi-

My TraceRoute (mtr). A network

callygroup hosts andnetworks.

diagnostictool used as an alterna-

NeTraMet.An opensource network

tive to the traditional traceroutepro-

gram.http://www.bitwizard.nl/mtr/.

flow analysistool available from

Seealso: traceroute/ tracert.

freshmeat.net/projects/netramet/

networkaddress. Thelowest IP

number in a subnet. Thenetwork

address is used in routing tables to

specifythe destination to be used

N connector. A sturdymicrowave

connectorcommonly found on out-

Glossary

403

NominalVoltage (VN). Theoperat-

whensending packets to a logical

group of IP addresses.

ingvoltage of a photovoltaicsystem,

typically 12 or 24 volts.

NetworkAddress Translation

(NAT).NAT is a networking technol-

ntop.A networkmonitoring tool that

ogythat allows many computers to

providesextensive detail aboutcon-

share a single, globally routable IP

nectionsand protocol use on a local

address. While NAT can help to

areanetwork. http://www.ntop.org/

solvethe problem of limited IP ad-

dressspace, it creates a technical

null. In an antennaradiation pattern,

challengefor two-way services,

a null is a zone in which theeffective

such as Voice over IP.

radiatedpower is at a minimum.

networkdetection. Networkdiag-

nulling.A specific case of multi-

nostictools that displayinformation

pathinterferencewhere the signal

aboutwireless networks, such as

at the receiving antenna is zeroed

thenetwork name, channel,and

by the destructiveinterference of

encryptionmethod used.

reflectedsignals.

networklayer.

Alsocalled the

number of days of autonomy(N).

Internetlayer. This is the thirdlayer

Themaximum number of daysthat

of the OSI and TCP/IPnetwork

a photovoltaic system canoperate

models,where IP operates and

withoutsignificantenergy received

Internetrouting takes place.

fromthe sun.

networkmask seenetmask

NumericalElectromagnetics

Code(NEC2). A freeantenna mod-

ngrep.An opensource network se-

elingpackage that lets youbuild an

curityutility used to find patterns in

antennamodel in 3D, and thenana-

dataflows.Available for freefrom

lyzethe antenna s electromagnetic

http://ngrep.sourceforge.net/

response.http://www.nec2.org/

node.Anydevice capable of send-

ingand receiving data on a network.

Accesspoints, routers,computers,

andlaptops are all examples of

OFDMseeOrthogonalFrequency

nodes.

DivisionMultiplexing

NominalCapacity (CN). Themaxi-

omnidirectionalantenna. An an-

mumamount of energy that can be

tennathat radiates almost equally in

extractedfrom a fully chargedbat-

everydirection in thehorizontal

tery. It is expressed in Ampere-hours

plane.See also: directionalan-

(Ah) or Watt-hours (Wh).

tenna,sectorial antenna

404

Glossary

one-armrepeater. A wirelessre-

overdischarge.Discharging a bat-

terybeyond its MaximumDepth of

peaterthat only uses a singleradio,

Discharge, whichresults in deterio-

at significantlyreduced throughput.

Seealso: repeater

ration of the battery.

onionrouting. A privacytool (such

oversubscribe.To allowmore users

as Tor) thatrepeatedly bouncesyour

thanthe maximum availableband-

TCPconnections across a number of

widthcan support.

serversspread throughout theInter-

net,wrapping routing information in a

number of encrypted layers.

OR logic. A logical operationthat

packet.On IP networks, messages

evaluates as true if any of theitems

sentbetween computers arebroken

beingcompared also evaluate as

intosmall pieces calledpackets.

true.See also: ANDlogic.

Eachpacket includes a source,des-

tination,and other routinginforma-

OrthogonalFrequency Division

tionthat is used to route it to its ulti-

Multiplexing(OFDM)

matedestination. Packets arereas-

sembledagain at the remote end by

OSInetwork model.

A popular

TCP(or another protocol)before

model of network communications

beingpassed to theapplication.

defined by the ISO/IEC 7498-1

packetfilter. A firewallthat oper-

standard.The OSI modelconsists

of seven interdependent layers,from

ates at the Internet layer by inspect-

thephysical through theapplication.

ingsource and destination IP ad-

Seealso: TCP/IPnetwork model.

dresses,port numbers, andproto-

cols. Packets are eitherpermitted

outboundtraffic. Networkpackets

or discarded depending on the

thatoriginate from the localnetwork

packetfilterrules.

andare bound for a destinationout-

sidethe local network(typically

partition.A techniqueused by net-

somewhere on the Internet). See

workhubs to limit the impact of

also:inboundtraffic.

computersthat transmitexcessively.

Hubswill temporarily removethe

overcharge.Thestate of a battery

abusivecomputer (partition it)from

whencharge is applied beyondthe

therest of the network, andrecon-

limit of the battery's capacity. If en-

nect it again after some time. Ex-

ergy is applied to a batterybeyond

cessivepartitioning indicatesthe

itspoint of maximum charge,the

presence of an excessive bandwidth

electrolytebegins to break down.

consumer,such as a peer-to-peer

Regulatorswillallow a small

client or network virus.

amount of overcharge time to a bat-

tery to avoid gasification, butwill

passivePOE injector seePower

removepower before the battery is

overEthernet

damaged.

Glossary

405

pathloss. Loss of radio signal due

PKI seePublicKey Infrastructure

to the distance betweencommuni-

plomb.A heavypiece of metal bur-

catingstations.

ied in the earth to improve a ground

PeakSun Hours (PSH). Average

connection.

value of daily irradiation for a given

PoEseePowerover Ethernet

area.

photovoltaicgenerator seesolar

point-to-multipoint.A wireless

panel

networkwhere several nodescon-

nectback to a central location.The

photovoltaicsolar energy. Theuse

classicexample of a point-to-

of solar panels to collectsolar en-

multipointnetwork is an access

ergy to produce electricity. Seealso:

point at an office with several lap-

thermalsolar energy

topsusing it for Internetaccess. See

also:point-to-point,multipoint-to-

photovoltaicsystem. An energy

multipoint

systemthat generates electricalen-

point-to-point.A wirelessnetwork

ergyfrom solar radiation andstores

it for later use. A standalonephoto-

consisting of only two stations,usu-

voltaicsystem does this withoutany

allyseparated by a greatdistance.

Seealso: point-to-multipoint,

connection to an established power

grid.See also: battery,solar panel,

multipoint-to-multipoint

regulator,load, converter,inverter

Point-to-PointProtocol (PPP). A

physicallayer. Thelowest layer in

networkprotocol typically used on

boththe OSI and TCP/IPnetwork

seriallines (such as a dial-upcon-

models. The physical layer is the

nection) to provide IP connectivity.

actualmedium used forcommunica-

polarplot. A graphwhere points are

tions,such as copper cable,optic

fiber, or radio waves.

located by projection along a rotat-

ingaxis (radius) to an intersection

pigtail.A shortmicrowave cable

withone of several concentriccir-

cles.See also: rectangularplot

thatconverts a non-standardcon-

nectorinto something morerobust

polarization.Thedirection of the

andcommonly available.

electriccomponent of an electro-

ping.A ubiquitousnetwork diagnos-

magneticwave as it leaves the

ticutility that uses ICMPecho re-

transmittingantenna. See also:

horizontalpolarization, vertical

questand reply messages to deter-

polarization, circular polarization

minethe round trip time to a network

host. Ping can be used to deter-

polarizationmismatch. A state

minethe location of networkprob-

lems by "pinging" computers in the

where a transmitting andreceiving

pathbetween the local machineand

antenna do not use the samepolari-

theultimate destination.

zation,resulting in signalloss.

406

Glossary

policy.In netfilter,the policy is the

throughthe use of filters.Privoxy is

oftenused in conjunction withTor.

defaultaction to be taken when no

otherfilteringrules apply. Forex-

proactiverouting. A meshimple-

ample,the default policy forany

chainmay be set to ACCEPT or

mentationwhere every nodeknows

DROP.

aboutthe existence of everyother

node in the mesh cloud as well as

portcounters. Managedswitches

whichnodes may be used to route

androuters provide statisticsfor

traffic to them. Each nodemaintains

eachnetwork port called portcount-

a routing table covering thewhole

meshcloud. See also:reactive

ers. These statistics mayinclude

routing

inboundand outbound packetand

bytecounts, as well as errorsand

protocolanalyzer. A diagnostic

retransmissions.

programused to observe anddisas-

power.Theamount of energy in a

semblenetwork packets. Protocol

certainamount of time.

analyzersprovide the greatestpos-

sibledetail about individualpackets.

Powerover Ethernet (PoE).A

protocolstack. A set of network

techniqueused to supply DC power

to devices using the Ethernetdata

protocolsthat provideinterdepend-

cable.See also: endspan injec-

entlayers of functionality. Seealso:

tors,mid spaninjectors

OSInetwork model andTCP/IP

networkmodel.

PPPseePoint to Point Protocol

PSHseePeakSun Hours

presentationlayer. Thesixth layer

Publickey cryptography. A form of

of the OSI networking model.This

layerdeals with datarepresentation,

encryptionused by SSL, SSH,and

such as MIME encoding or data

otherpopular securityprograms.

compression.

Publickey cryptography allowsen-

cryptedinformation to be exchanged

privateaddress space. A set of

over an untrusted networkwithout

reserved IP addresses outlined in

theneed to distribute a secretkey.

RFC1918.Private address space is

PublicKey Infrastructure (PKI).A

frequentlyused within an organiza-

tion, in conjunction withNetwork

securitymechanism used in con-

junctionwith publickey cryptogra-

AddressTranslation (NAT).

The

phyto preventthe possibility of

reservedprivate address space

Man-In-The-Middleattacks.See

ranges include 10.0.0.0/8,

also:certificateauthority

172.16.0.0/12,and 192.168.0.0/16.

Seealso: NAT.

Privoxy(http://www.privoxy.org/). A

webproxy that providesanonymity

Glossary

407

dressesare administered by the

IANA.The space has beendivided

intolarge subnets, which aredele-

gated to one of the five regional

quickblow. A type of fuse that im-

Internetregistries, each withauthor-

mediatelyblows if the current flow-

ityover a large geographicarea.

ingthrough it is higher thantheir

rating.See also: slowblow

regulator.Thecomponent of a pho-

tovoltaicsystem thatassures that

thebatteryis working in appropriate

conditions. It avoids overcharging

or underchargingthebattery, both

radiationpattern seeantenna

of which are very detrimental to the

pattern.

life of the battery. See also:solar

panel,battery, load,converter,

radio.Theportion of theelectro-

inverter

magneticspectrum in whichwaves

can be generated by applyingalter-

repeater.A nodethat is configured

natingcurrent to an antenna.

to rebroadcast traffic that is not des-

tinedfor the node itself,often used

reactiverouting. A meshimple-

to extend the useful range of a net-

mentationwhere routes arecom-

work.

putedonly when it is necessary to

senddata to a specific node.See

Requestfor Comments(RFC).

also:proactiverouting

RFCsare a numbered series of

documentspublished by theInternet

realtimemonitoring. A network

Societythat document ideasand

monitoringtool that performsunat-

conceptsrelated to Internettech-

tendedmonitoring over longperiods,

nologies. Not all RFCs areactual

andnotifies administrators immedi-

standards,but many are eitherap-

atelywhen problems arise.

provedexplicitly by the IETF, or

eventuallybecome de facto stan-

reciprocity.An antenna'sability to

dards.RFCs can be viewedonline

maintainthe samecharacteristics

at http://rfc.net/.

regardless if whether it is transmit-

ting or receiving.

returnloss. A logarithmicratio

measured in dB that comparesthe

recombinantbatteries seelead-

power reflected by the antenna to

acidbatteries

thepower that is fed intothe an-

tennafrom the transmissionline.

rectangularplot. A graphwhere

Seealso: impedance

pointsare located on a simplegrid.

Seealso: polarplot

reversepolarity (RP). Proprietary

microwaveconnectors, based on a

RegionalInternet Registrars

standardconnector but withthe

(RIR).The 4 billion available IP ad-

gendersreversed. The RP-TNCis

408

Glossary

probablythe most commonreverse

forwarded. If a router receives a

polarityconnector, but others(such

packetfor a network that is not in

as RP-SMA and RP-N) arealso

therouting table, the routeruses its

commonplace.

defaultgateway. Routers operate at

theNetwork Layer.

Seealso:

RF transmission line. Theconnec-

bridgeanddefaultgateway.

tion(typically coax, Heliax, or a

waveguide) between a radio and an

RP seeReversePolarity

antenna.

RP-TNC.A commonproprietary

RIRseeRegionalInternet Regis-

version of the TNC microwavecon-

trars

nector,with the gendersreversed.

TheRP-TNC is often found on

R o u n d Tr i p T i m e ( RT T ) . T h e

equipment manufactured by

amount of time it takes for a packet

Linksys.

to be acknowledged from theremote

RRDseeRoundRobin Database

end of a connection.

Frequently

confusedwith latency.

RRDtool.A suite of tools that allow

rogueaccess points. An unauthor-

you to create and modify RRDdata-

bases, as well as generateuseful

izedaccess point incorrectlyin-

graphs to present the data.

stalled by legitimate users, or by a

RRDtool is used to keep track of

maliciousperson who intends to

time-seriesdata (such as network

collectdata or do harm to thenet-

bandwidth,machine room tempera-

work.

ture, or server load average)and

RoundRobin Database (RRD).A

candisplay that data as an average

overtime. RRDtool is availablefrom

databasethat stores information in a

http://oss.oetiker.ch/rrdtool/

verycompact way that doesnot ex-

pandover time. This is thedata

rsync(http://rsync.samba.org/). An

formatused by RRDtool andother

networkmonitoring tools.

opensource incremental file transfer

utilityused for maintainingmirrors.

router.

A device that forwards

RTTseeRoundTrip Time

packetsbetween differentnetworks.

Theprocess of forwardingpackets

to the next hop is calledrouting.

routing.Theprocess of forwarding

packetsbetween differentnetworks.

SACKseeSelectiveAcknowl-

A device that does this is called a

edgment

router.

scattering.Signalloss due to ob-

routingtable. A list of networks

jects in the path between twonodes.

and IP addresses kept by a router to

Seealso: freespace loss,at-

determinehow packets should be

tenuation

Glossary

409

sectorialantenna. An antennathat

sharedmedium. A link-localnet-

radiatesprimarily in a specific area.

workwhere every node canobserve

Thebeam can be as wide as 180

thetraffic of everyother node.

degrees, or as narrow as 60 de-

grees.See also: directionalan-

Shorewall(http://shorewall.net/). A

tenna,omnidirectional antenna

configurationtool used for setting up

netfilterfirewallswithout the need to

SecureSockets Layer (SSL).An

learniptables syntax.

end-to-endencryption technology

sidelobes.No antenna is able to

builtinto virtually all webbrowsers.

SSLuses publickey cryptography

radiateall the energy in onepre-

and a trusted publickey infra-

ferreddirection. Some is inevitably

structureto securedata communi-

radiated in other directions.These

cations on the web. Wheneveryou

smallerpeaks are referred to as

visit a web URL that startswith

sidelobes.

https,you are usingSSL.

signalgenerator. A transmitterthat

Selective Acknowledgment (SACK).

emitscontinuously at a specific fre-

A mechanism used to overcome

quency.

TCPinefficiencies on high latency

SimpleNetwork Management

networks,such as VSAT.

Protocol (SNMP). A protocolde-

ServerMessage Block (SMB). A

signed to facilitate the exchange of

managementinformation between

networkprotocol used in Windows

networkdevices. SNMP is typically

networks to provide file sharing

services.See also: NetBIOS.

used to poll network switchesand

routers to gather operatingstatistics.

ServiceSet ID (SSID) seeEx-

tendedService Set Identifier

site-wideweb cache. Whileall

modernweb browsers provide a

sessionlayer. Layerfive of theOSI

localdata cache, largeorganizations

model,the Session Layermanages

canimprove efficiency by installing a

logicalconnections betweenappli-

site-wideweb cache, such as Squid.

cations.

A site-wide web cache keeps a copy

of all requests made fromwithin an

sessionoriented protocol. A net-

organization,and serves thelocal

workprotocol (such as TCP)that

copy on subsequent requests.See

also:Squid.

requiresinitialization beforedata

can be exchanged, as well as some

slowblow. A fusethat allows a cur-

clean-upafter data exchangehas

completed.Session orientedproto-

renthigher than its rating to pass for

a short time. See also:quickblow

colstypically offer errorcorrection

andpacket reassembly, whilecon-

SMA.A smallthreaded microwave

nectionlessprotocols do not. See

also:connectionlessprotocol.

connector.

410

Glossary

SMBseeServerMessage Block

shouldhave low latency andmore

thanenough capacity to carrythe

SmokePing. A latency measure-

traffic of its users. See also:band-

width, capacity, andlatency.

menttool that measures, storesand

displayslatency, latencydistribution

splithorizon DNS. A technique

andpacket loss all on a single

graph.SmokePing is availablefrom

used to serve different answers to

http://oss.oetiker.ch/smokeping/

DNSrequests based on thesource

of the request. Split horizon is used

SNMP seeSimpleNetwork Man-

to direct internal users to a different

agementProtocol

set of servers than Internetusers.

Snort(http://www.snort.org/). A

spoof.To impersonate a network

verypopular open sourceintrusion

device,user, or service.

detectionsystem. See also:Intru-

spotcheck tools. Networkmoni-

sionDetection System.

toringtools that are runonly when

SoCseeState of Charge

needed to diagnose a problem.

Pingand traceroute are examples of

solarmodule seesolarpanel

spotcheck tools.

Squid.A verypopular open source

solarpanel. Thecomponent of a

photovoltaicsystem used to con-

webproxy cache. It is flexible,ro-

bust,full-featured, and scales to

vertsolar radiation intoelectricity.

Seealso: battery,regulator, load,

supportnetworks of nearly anysize.

converter,inverter

http://www.squid-cache.org/

solarpanel array. A set of solar

SSIDseeExtendedService Set

panelswired in series and/or paral-

Identifier

lel in order to provide thenecessary

SSLseeSecureSockets Layer

energyfor a given load.

standalonephotovoltaic system

solarpower charge regulatorsee

seephotovoltaicsystem

regulator

S t a t e o f C h a rg e ( S o C ) . T h e

spectrumseeelectromagnetic

spectrum

amount of charge present in a bat-

tery,determined by the currentvolt-

spectrumanalyzer. A devicethat

ageand type of battery.

provides a visual representation of

statefulinspection. Firewallrules

theelectromagnetic spectrum.See

also:Wi-Spy

thatare aware of the thestate asso-

ciatedwith a given packet. Thestate

Speed.A genericterm used to refer

is not part of the packet as transmit-

tedover the Internet, but is deter-

to the responsiveness of a network

mined by the firewallitself. New,

connection. A "high-speed" network

Glossary

411

clude ACCEPT, DROP, LOG, and

established,and relatedconnections

REJECT.

mayall be taken intoconsideration

whenfilteringpackets. Statefulin-

TCPseeTransmissionControl

spection is sometimes calledcon-

Protocol

nectiontracking.

stationarybatteries. Batteriesde-

TCPacknowledgment spoofing

signed to have a fixedlocation and

TCPwindow size. TheTCP pa-

in scenarios where the powercon-

sumption is more or lessirregular.

rameterthat defineshow much data

Stationarybatteries canaccommo-

thatmay be sent before an ACK

datedeep discharge cycles, butthey

packet is returned from thereceiving

arenot designed to producehigh

side.For instance, a window size of

currents in brief periods of time.See

3000would mean that twopackets

also:lead-acidbatteries

of 1500 bytes each will be sent, after

whichthe receiving end willeither

structure.In NEC2, a numerical

ACKthe chunk or requestretrans-

description of where thedifferent

mission.

parts of the antenna arelocated,

TCP/IPseeInternetprotocol suite

andhow the wires areconnected

up.See also: controls

TCP/IPnetwork model. A popular

subnetmask seenetmask

simplification of the OSI network

modelthat is used with Internetnet-

subnets.A subset of a range of IP

works.The TCP/IP modelconsists

networks, defined by netmasks.

of five interdependent layers,from

thephysical through theapplication.

switch.

Seealso: OSInetwork model.

A network device thatpro-

vides a

temporary,dedicated con-

tcpdump. A popular open source

nection

betweencommunicating

Seealso: hub.

devices.

packetcapture and analysistool

available at http://www.tcpdump.org/.

switchingconversion. A DC volt-

Seealso: WinDumpandWireshark.

ageconversion method that uses a

TemporalKey IntegrityProtocol

magneticcomponent to temporarily

(TKIP).An encryptionprotocol used

storethe energy and transform it to

in conjunction with WPAto improve

anothervoltage. Switchingconver-

sion is much more efficientthan lin-

thesecurity of a communications

earconversion.

session.

thermalsolar energy. Energycol-

lectedfrom the sun in theform of

heat.See also: photovoltaicsolar

energy

target.In netfilter,the action to be

takenonce a packet matches a rule.

Somepossible netfiltertargets in-

412

Glossary

thrashing.Thestate when a com-

traceroute / tracert. A ubiquitous

puterhas exhausted theavailable

networkdiagnostic utility oftenused

RAMand must use thehard disk for

in conjunction with ping to determine

temporarystorage, greatlyreducing

thelocation of networkproblems.

systemperformance.

The Unix version is called

traceroute,while the Windowsver-

throughput.Theactual amount of

sion is tracert. Both use ICMPecho

informationper second flowing

requestswith increasing TTLvalues

through a network connection,dis-

to determine which routers areused

regardingprotocol overhead.

to connect to a remote host,and

alsodisplay latency statistics. An-

throughputtesting tools. Tools

othervariant is tracepath,which

thatmeasure the actualbandwidth

uses a similar technique withUDP

packets.See also: mtr.

availablebetween two points on a

network.

tractionbatteries seelead-acid

Time To Live (TTL). A TTLvalue

batteries

acts as a deadline or emergency

TransmissionControl Protocol

brake to signal a time when thedata

(TCP).A sessionoriented protocol

should be discarded. In TCP/IPnet-

works,the TTL is a counterthat

thatoperates at the TransportLayer,

starts at some value (such as 64)

providingpacket reassembly,con-

and is decremented at eachrouter

gestionavoidance, and reliablede-

hop. If the TTL reacheszero, the

livery. TCP is an integralprotocol

packet is discarded. Thismecha-

used by many Internetapplications,

nismhelps reduce damagecaused

includingHTTP and SMTP.

See

also:UDP.

by routing loops. In DNS, theTTL

definesthe amount of time that a

transmissionpower. Theamount

particularzone record should be

keptbefore it must be refreshed. In

of power provided by theradio

Squid,the TTL defineshow long a

transmitter,before any antennagain

cachedobject may be kept before it

or line losses.

must be again retrieved fromthe

transparentbridging firewall. A

originalwebsite.

firewalltechnique that introduces a

TKIPseeTemporalKey Integrity

bridgethat selectivelyforwards

Protocol

packetsbased on firewallrules.

Onebenefit of a transparent bridg-

TNCconnector. A common,sturdy

ingfirewall is that it does notrequire

an IP address. See also:bridge.

threadedmicrowave connector.

Tor(http://www.torproject.org/). An

transparentcache. A method of

onionrouting toolthat provides

implementing a site-wide web cache

goodprotection against traffic

thatrequires no configuration on the

analysis.

webclients. Web requestsare si-

lentlyredirected to the cache,which

Glossary

413

makesthe request on behalf of the

client. Transparent cachescannot

useauthentication, which makes it

impossible to implement traffic ac-

U.FL.A verytiny microwave con-

counting at the user level. Seealso:

nectorcommonly used on mini-PCI

site-wideweb cache, Squid.

radiocards.

transparentproxy. A cachingproxy

UDP seeUserDatagram Protocol

installed so that users webrequests

areautomatically forwarded to the

unintentionalusers. Laptopusers

proxyserver, without any need to

whoaccidentally associate to the

manuallyconfigureweb browsers to

wrongwireless network.

useit.

UnshieldedTwisted Pair(UTP).

transportlayer. Thethird layer of

Cableused for 10baseTand

theOSI and TCP/IP networkmod-

100baseTEthernet, consisting of

els,which provides a method of

fourpairs of twistedwires.

reaching a particular service on a

givennetwork node. Examples of

UsefulCapacity (Cu ). Theusable

protocolsthat operate at thislayer

capacity of a battery, equal to the

areTCPandUDP.

product of the NominalCapacity

andthe MaximumDepth of Dis-

trending.A type of network monitor-

charge.

ingtool that performsunattended

monitoringover long periods,and

UserDatagram Protocol(UDP). A

plotsthe results on a graph.Trend-

connectionlessprotocol (atthe

ingtools allow you to predictfuture

transportlayer) commonlyused for

behavior of your network,which

videoand audio streaming.

helpsyou plan for upgradesand

changes.

UTPseeUnshieldedTwisted Pair

TTLseeTime To Live

tunnel. A form of data encapsula-

tionthat wraps one protocolstack

valveregulated lead acidbattery

withinanother. This is often used in

(VRLA) seelead-acidbatteries

conjunctionwith encryption to pro-

tectcommunications frompotential

verticalpolarization. An electro-

eavesdroppers,while eliminating the

magneticfieldwith the electriccom-

need to support encryptionwithin

ponentmoving in a linearvertical

theapplication itself. Tunnelsare

direction.Most wirelessconsumer

oftenused conjunction withVPNs.

electronicdevices use verticalpo-

larization.See also: circular polari-

zation,vertical polarization

414

Glossary

VerySmall ApertureTerminal

Seealso: BroadbandGlobal Ac-

(VSAT).One of several standards

cessNetwork (BGN) andDigital

VideoBroadcast (DVB-S).

usedfor satellite Internetaccess.

VSAT is the most widelydeployed

satellitetechnology used in Africa.

Seealso: BroadbandGlobal Ac-

cessNetwork (BGAN) andDigital

VideoBroadcast (DVB-S).

WANseeWideArea Network

videosender. A 2.4GHz video

War drivers. Wirelessenthusiasts

transmitterthat can be used as an

whoare interested in findingthe

inexpensivesignalgenerator.

physicallocation of wirelessnet-

works.

VirtualPrivate Network (VPN).A

wavelength.Thedistance meas-

toolused to join two networksto-

getherover an untrustednetwork

uredfrom a point on one wave to

(such as the Internet). VPNsare

theequivalent part of the next,for

oftenused to connect remoteusers

examplefrom the top of onepeak to

to an organization's networkwhen

thenext. Also known as lambda ( ).

traveling or working from home.

VPNsuse a combination of encryp-

WEPseeWiredEquivalent Privacy

tionand tunneling to secure allnet-

worktraffic, regardless of the appli-

wget. An opensource command

cationbeing used. See also:tun-

linetool for downloading webpages.

nel.

http://www.gnu.org/software/wget/

VoIP(Voiceover IP). A technology

Wi-Fi.A marketingbrand owned by

thatprovides telephone-likefeatures

theWi-Fi Alliance that is used to

over an Internet connection.Exam-

refer to various wirelessnetworking

ples of popular VoIP clientsinclude

technologies(including 802.11a,

Skype,Gizmo Project, MSN Mes-

802.11b,and 802.11g). Wi-Fi is

senger,and iChat.

shortfor WirelessFidelity.

VPNseeVirtualPrivate Network.

Wi-FiProtected Access (WPA). A

fairlystrong link layer encryption

VRLAseevalveregulated lead

protocolsupported by mostmodern

acidbattery

Wi-Fiequipment.

VSATseeVerySmall Aperture

Wi-Spy.An inexpensive2.4 GHz

Terminal

spectrumanalysis toolavailable

fromhttp://www.metageek.net/.

VerySmall ApertureTerminal

(VSAT).One of several standards

WideArea Network (WAN).Any

usedfor satellite Internetaccess.

longdistance networkingtechnol-

VSAT is the most widelydeployed

ogy.

Leasedlines, frame relay,

satellitetechnology used in Africa.

DSL,fixedwireless, and satelliteall

Glossary

415

typicallyimplement wide areanet-

works.See also: LAN.

wiki.A website that allows anyuser

to edit the contents of anypage.

One of the most popular publicwikis

is http://www.wikipedia.org/

windowscale. A TCPenhancement

defined by RFC1323 thatallows

TCPwindow sizes larger than64KB.

WinDump.TheWindows version of

tcpdump.

It is available from

http://www.winpcap.org/windump/

WiredEquivalent Privacy (WEP).A

somewhatsecure link layer en-

cryptionprotocolsupported by vir-

tuallyall 802.11a/b/gequipment.

WirelessFidelity seeWi-Fi.

wireshark.A freenetwork protocol

analyzerfor Unix andWindows.

http://www.wireshark.org/

WPAseeWi-FiProtected Access

Zabbix(http://www.zabbix.org/) A

realtimemonitoring tool thatlogs

andnotifies a systemadministrator

aboutservice and networkoutages.

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